The massive Fort that runs round the settlement like a girdle, dates back to 1559 AD. About 30,000 sq. mt with ten bastions and two gateways, the fort is well protected by a moat on the land side and also connects the river to the sea.

Basically polygonal in plan with projections at regular intervals of about 500 ft. it carries splayed angular bastions. It contains loop holes, but no merlons. The terraces close to the top of the wall are connected to the inner ground surface by an open flight of steps at many places. All along the inner wall, there are barracks for defense personnels.  

The inscription above the Southern (land) gate mentions that this gate along with the bastions adjacent to it was completed in 1581 AD, after the Mughal invasion in Akbar's reign. The inscription on the Northern (sea) gate gives the date of 1593 AD for the completion of the Fort wall. On the Northern side within the confine of the fort were located the palaces, the Secretariat and other official buildings.